Electron apparatus



Jan. 16, 1940. w. H. MANTHORNE ELECTRON APPARATUS.

Filed Jan. 8, 1938 INVENTOR W H. MANTHORNE A TTORNEY Patented Jan. 16, 1940 UNITED STATEfi iATENT OFFICE ELECTRON APlPARATUS Application January 8, 1938, Serial No. 183,962

1 Claim.

This invention relates to electron apparatus and more particularly to vacuum tubes in which is employed an electron stream emanant from a heated filament and passing through a grid.

Vacuum tubes having a heated filament and a. grid together with other electrical elements have a great variety of uses and are made in a great number of difierent designs, forms and sizes. All of these, which have the heated filament to produce an electron stream, have a useful life which, barring accident, is terminated by the eventual failure of the heated filament which evaporates slowly under service conditions.

An object of the present invention is to provide means whereby the physical. state of one oi the elements of a vacuum tube may be tested either continuously or from time to time, while the tube which contains it is in service, and so detect an approaching failure of the filament before it occurs, that the tube may be replaced by another with the minimum of disruption of operation of apparatus in which the tube may be serving.

With the above and other objects in view the invention may be embodied in a vacuum tube having a heatable filament, a regular service grid associated therewith and an auxiliary testing grid also associated with the filament and insulated or insulatable from the regular grid.

Other objects and features of the invention will appear from the following detailed description of embodiments thereof taken. in connection with the accompanying drawing in which the same reference numerals are applied to identical parts in the several figures and in which Fig. 1 is a view in perspective of a vacuum tube constructed in accordance with the invention with a portion of the body broken away, and

Fig. 2 is a partial similar view of a modified form.

The embodiment of the invention disclosed in Fig. 1 presents a vacuum tube which may be generally of any desired and appropriate construction and combination of parts and which comprises also the following features characteristic of the invention. There is a heatable filament 2!] consisting of a metal strand or wire formed into one or more usually coplanar waves or loops, as shown, which are supported by suitable means, such as the conventional hooks 2|, within the hollow body 22 of the tube. The body 22 may be of glass, metal, or other material as desired.

A grid, generally indicated at 24, consists of two upright metal posts 25, suitably supported.

with a pair of fiat helices 26 and ii of wire coiled around and supported on and electrically one with the posts. The parts of the grid 24 are so proportioned and arranged that the helix surrounds the lower portions of the loops of the filament 2t, and. the helix 2l similarly encloses the upper portions of the filament loops, the helices 26 and 27 being spaced from each other on the posts 25 so that the central portions of the filamentv are not within any coils of the grid 2 An auxiliary grid, generally indicated at 30, consists of two upright metal posts 3!, suitably supported, with a single fiat helix 320i wire coiled and supported on and electrically one with these posts. These parts are so proportioned and arranged that the helix 32 surrounds the central portions of the loops of the filament which are not within. any coils of the grid 24.

These electrical elements of the tube, viz., the

filament 23, the grid 24 and the auxiliary grid 39, are suitably supported within the evacuated body 20 of the tube in any appropriate fashion and have connections to terminals outside of the body as is customary in such devices. These supports and connections and terminals, being familiar in the art and being as to structure and arrangement no part of the present invention, are not further particularized here. The tube may also contain other electrical elements to coact with those shown, e. g., plate, screens, and the like, but these are not relevant to the present invention and so are omitted from the drawing to make for greater clarity. However, if the body 220i the tube be of metal, it may be used as the plate of a complete triode tube, in which case Fig. 1 shows a complete and operative device.

It is found that in use, the most active and generally hottest part of the filament 20 is the middle portions of its loops, shown as surrounded by the helix 32 of the grid an.

Generally, the grid 30 is completely insulated from the grid 24 and is connected thereto outside of the tube to make the two grids electrically one, for the ordinary operation of the tube. The grid 30 may then be connected also, independently of the grid 24, into an auxiliary testing circuit independent of whatever operating circuits the grid 24 alone or the grids 24 and 30 together may be a part of.

Such a test circuit including the grid 3!! alone, as shown at the bottom of Fig. 1, may then be used to give information from time to time or continuously, as desired, as to the state of the filament; for, with a constant heating current applied to the filament the temperature of and hence the volume of electrons emitted by the filament will rise when and as the filament is wasted by service. For a given size of filament and normal temperature of its operation, there can easily be determined a danger or warning point of unusual or excessive temperature which betokens the probability that the filament will burn out within a shortperiod, and that it is time to switch in a substitute tube in place of the one in use before failure occurs.

In the embodiment disclosed in Fig. 2, there is a vacuum tube having a hollow evacuated body within which is mounted, in any appropriate way, a filament 20, here shown as having only one loop but which may equally well have a plurality of loops as in Fig. 1. A stationary regular grid, generally shown at 24, has two metallic posts supported and electrically connected to an outside terminal in any appropriate way. The grid 24 is completed by a single flat helix 2B of Wire, extending substantially from end to end of the posts 25, electrically one with the posts, and enclosing a major portion of the filament 20. An auxiliary grid 38 consists of posts 3! and helix 32 of wire on the posts and surrounds both the grid 24 and the filament 2% inside the grid 26.

The posts 3! of the grid 3!) are mounted on a support 33 which in turn is mounted on a device whose function is to move the support 33 and therewith the grid up and down Within the body and thus render the grid 30 adjustable along the grid 24. The device is adjustable to efiect this result by means of the knurled rotatable sleeve35. The nature and construction of the device are no part of the present invention but will be found fully disclosed and described in detail in copending application Serial Number 183,961'filed January 8, 1938, by the present inventor.

In this construction the auxiliary grid 30 may be used, as before, to test the condition and emissivity of the filament, to detect symptoms of approaching failure of the filament, to study variations of emissivity along the filament, and for other similar purposes. It will not be as sensitive to detect approaching failure in some cases as is the previous arrangement because of the interposition of the regular grid 24, but in many cases may be sufiiciently so for actual use. On the other hand a given filament may be searched with this auxiliary grid along its length and maximum emissivity found at some point other than normal. In such a case this is the probable site of eventual failure of the filament, and the auxiliary grid can then be left there to detect the first symptoms of failure.

As before, only those elements of the tube directly relevant to the invention are shown, but again if the body 22 be thought of as metal, there is presented a complete operative triode tube.

Obviously, if the filament or the regular grid or both have forms or arrangements other than exactly as herein disclosed, modification in form or arrangement or both of the auxiliary grid may be required, but it is thought that such will be self evident in each case to those skilled in the art, and the illustrative embodiments herein shown may be modified and departed from in various ways without departing from. the spirit and scope of the invention as pointed out in and limited only by the appended claim.

What is claimed is:

A vacuum tube having a filament and means to determine emissivity of various parts of the filament and to detect an abnormal state of the filament, the said means consisting of a grid 00- acting with the filament and movable longitudinally along the same, and electrical means connected to the grid and to the filament to measure emission of electrons by the filament. 40

WILLIAM H. MAN'IHORNE. 

